1. Field of the Invention
The present invention relates to an improved structure of a pivotal-shaft receiving hole in a molded product having a thin wall such as a magnetic tape cassette.
2. Description of the Prior Arts
A product having a thin wall is generally fabricated by injection molding of synthetic resin. When a pair of molded products which are to be assembled with a pivotal connection are prepared, a pair of pivotal-shafts are formed in one piece and a pair of holes for receiving the shaft are formed in the other piece and both pieces are assembled by fitting the pivotal-shafts into each of the holes so as to be pivotally moved. However, with a metallic mold pattern which produces, in injection molding of a synthetic resin, a through hole in a wall, a "burr" in a film form will be produced at the opening of the hole at the inlet portion or the opening at the outlet portion. It is quite difficult or impossible to form a through hole without any burr.
When the wall thickness of the molded product is substantially large and the depth of the hole for receiving the pivotal shaft is greater than the length of the pivotal-shaft, it is necessary to remove the burr in a film form produced at the inlet portion of the through hole whereas the burr at the outlet portion causes no trouble. Accordingly, when a thick-walled molded product is produced, a metallic molding pattern is so formed that the burr in a film form is produced at the outlet portion of the through hole, thus resulting in no trouble. However, in a thin-walled molded product such as a magnetic tape cassette, the pivotal-shaft is made longer than the through hole so that the shaft passes through the hole in order to provide a rigid shaft-hole fitting structure. In such a case, a problem of thin-film burr produced at the inlet and outlet portions arises. This problem has been overcome by removing the film-like burr produced at the inlet and outlet portions of the hole by machining to allow the pivotal-shaft to pass through the hole for receiving the shaft in assembling. However, with this process, a complicated machining is required resulting in decrease of productivity.